Multilayer films and sealed packages made from these films

ABSTRACT

Multilayer Films have a first skin layer that is prepared from a high density polyethylene and a second skin layer (also referred to as the sealant layer) that is prepared from a linear low density polyethylene (LLDPE) having a density of from 0.90 to 0.92 g/cc and a Dilution Index, Yd, of greater than 0°. Seals can be prepared by placing two pieces of this film against each other such that the sealant layers are in contact with each other, then applying heat to at least one high density skin layer such that heat is transmitted/conducted through the multilayer film in a sufficient amount to melt the sealant layer and form a seal. The use of LLDPE having a Dilution Index of greater than 0° has been found to improve the sealing performance of multilayer films in comparison to multilayer films where the sealant layer is a conventional LLDPE having a Dilution Index of less than 0°.

TECHNICAL FIELD

Provided herein are multilayer, recyclable polyethylene films withimproved sealing performance and packages made from these films.

BACKGROUND ART

Simple, inexpensive and recyclable polyethylene packages may be easilyprepared by heat sealing together two layers of polyethylene to form aproduct known as a “pillow pack” to those skilled in the art. Pillowpackages do not provide the stiffness/rigidity which is desirable forhigher quality packages, such as Stand Up Pouch (SUP) packages; someForm-Full-Seal (FFS) packages or embossed packages. These higherquality/more rigid packages are typically made with a layer of a stifferpolymer (such as polyester or polyamide) and this makes thesemultilayer/multicomponent films difficult to recycle because it is notpossible to easily separate the polyethylene layer from the polyester(or polyamide) layer in current recycling facilities.

More recently, “all polyethylene” film structures for use in themanufacture of stand up pouches have become available. These films needto be carefully designed to give the right performance as a finishedpackage, and to be “processable” on the equipment that converts thefilms to packages at high production rates.

Forming seals in these pouches poses a challenge because the heat energyneeded to form a hermetic seal can be too high for the film structure tosurvive. The films should offer a low SIT (seal initiation temperature)and good “caulkability” (i.e. the ability to form seals throughcontamination and to allow the sealant to flow to prevent pinholeleaks).

One problem when preparing sealed packages on a Form/Fill/Seal (FFS)packaging machine is to produce a good hermetic seal at the base of thepouch.

Some known films address this problem by using a layer of polyester(PET) and a layer of polyethylene (PE). The PET layer does not soften asmuch as the PE during the sealing process because it has a meltingtemperature higher than 200° C., but the polyethylene does melt and flowto form the seal. However, as noted above, these films (and packagesmade from them) are difficult to recycle.

Polyethylene melts at much lower temperatures, which limits the maximumsealing bar temperature to around 150° C. Above that, the film materialis likely to “burn through”.

It is known to prepare “all PE” multilayer films having a high densityskin layer (which melts at a temperature of from 130 to 135° C.) and asealant layer made from a single site catalyzed, linear low densitypolyethylene (SSC-LLDPE) having a lower melting point. The sealing baris applied to the high density skin layer and heat is conducted throughthe film structure to the sealant layer (the second skin) to form theseal.

SUMMARY OF INVENTION

Disclosed herein are improved films—which allow for the preparation ofhigh quality seals at high production rates—that can be prepared byusing a linear low density polyethylene having a dilution index, Yd, ofgreater than 0°. These polyethylenes may be prepared using a dualcatalyst system as described in U.S. Pat. No. 9,512,282 (Li et al. toNOVA Chemicals Corporation).

In an embodiment, provided herein is a multilayer film comprising:

a) a first skin layer consisting of from 85 to 100 weight % of a highdensity polyethylene having a density of from 0.95 to 0.97 g/cc and amelt index, I₂, of from 0.5 to 10 g/10 minutes;

b) a second skin layer consisting of from 85 to 100 weight % of a firstlinear low density interpolymer having a molecular weight distributionM_(w)/M_(n) of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, amelt index, I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd,of greater than 0°; and

c) a core comprising polyethylene,

with the proviso that the polymeric material used to prepare saidmultilayer film is at least 90% by weight polyethylene based on thetotal weight of said polymeric material.

In another embodiment, provided herein is a multilayer film comprising:

a) a first skin layer consisting of from 85 to 100 weight % of a highdensity polyethylene having a density of from 0.95 to 0.97 g/cc and amelt index, I₂, of from 0.5 to 10 g/10 minutes;

b) a second skin layer consisting of from 85 to 100 weight % of a firstlinear low density interpolymer having a molecular weight distributionM_(w)/M_(n) of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, amelt index, I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd,of greater than 0°; and

c) a core comprising at least one layer of linear low densitypolyethylene, having a density of from 0.90 to 0.92 g/cc;

with the proviso that the polymeric material used to prepare saidmultilayer film is at least 90% by weight polyethylene based on thetotal weight of said polymeric material.

In another embodiment, provided herein is a multilayer film comprising:

a) a first skin layer consisting of from 85 to 100 weight % of a highdensity polyethylene having a density of from 0.95 to 0.97 g/cc and amelt index, I₂, of from 0.5 to 10 g/10 minutes;

b) a second skin layer consisting of from 85 to 100 weight % of a firstlinear low density interpolymer having a molecular weight distributionM_(w)/M_(n) of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, amelt index, I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd,of greater than 0°; and

c) a core comprising at least one layer of medium density polyethylenehaving a density of from 0.930 to 0.945 g/cc,

with the proviso that the polymeric material used to prepare saidmultilayer film is at least 90% by weight polyethylene based on thetotal weight of said polymeric material.

In another embodiment, provided herein is a process to make a sealedpackage with a multilayer film comprising:

a) a first skin layer consisting of from 85 to 100 weight % of a highdensity polyethylene having a density of from 0.95 to 0.97 g/cc and amelt index, I₂, of from 0.5 to 10 g/10 minutes;

b) a second skin layer consisting of from 85 to 100 weight % of a firstlinear low density interpolymer having a molecular weight distributionM_(w)/M_(n) of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, amelt index, I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd,of greater than 0°; and

c) a core comprising polyethylene,

with the proviso that the polymeric material used to prepare saidmultilayer film is at least 90% by weight polyethylene based on thetotal weight of said polymeric material;

-   said process comprising forming a package structure by placing a    first layer of said multilayer film on top of a second layer of said    multilayer film such that the second skin layer of said first layer    is in contact with said second skin layer; applying heat and    pressure to at least one of said first skin layer of said first    layer and said second skin layer of said second layer wherein said    heat and pressure is sufficient to melt bond said second skin layer    of said first layer to said second skin layer of said second layer.

In another embodiment, provided herein is a multilayer film comprising:

a) a first skin layer consisting of from 85 to 100 weight % of a highdensity polyethylene having a density of from 0.95 to 0.97 g/cc and amelt index, I₂, of from 0.5 to 10 g/10 minutes;

b) a second skin layer consisting of from 85 to 100 weight % of a firstlinear low density interpolymer having a molecular weight distributionM_(w)/M_(n) of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, amelt index, I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd,of greater than 0°; and

c) a core comprising medium density polyethylene having a density offrom 0.930 to 0.945 g/cc,

with the proviso that the polymeric material used to prepare saidmultilayer film is at least 90% by weight polyethylene based on thetotal weight of said polymeric material. In another embodiment, providedherein is a stand up pouch made according to this process.

The films of this invention contain at least 90 weight % (especially atleast 95 weight %) of polyethylene, based on the total weight ofpolymeric material in the film, to allow for recycling.

The first skin layer in all films consists of from 85 to 100 weight % ofspecified high density polyethylene, based on the weight of polymericmaterial in the skin layer. In general, this skin layer may be 100weight % of the specified high density polyethylene although minoramounts (up to 15 weight %) of other polymers (especially otherpolyethylene polymers) may be included.

The second skin layer in all films consists of from 85 to 100 weight %of specified LLDPE (having a dilution index, Yd, of greater than 0°)based on the weight of polymeric material in the second skin layer. Ingeneral, this skin layer may be 100% of the specified LLDPE althoughminor amounts (up to 15 weight %) of other polymers (especially otherpolyethylene polymers) may be included.

DESCRIPTION OF EMBODIMENTS Definition of Terms

Other than in the examples or where otherwise indicated, all numbers orexpressions referring to quantities of ingredients, extrusionconditions, etc. used in the specification and claims are to beunderstood as modified in all instances by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that can vary depending upon the desired properties thatthe various embodiments desire to obtain. At the very least, and not asan attempt to limit the application of the doctrine of equivalents tothe scope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques. The numerical values set forth inthe specific examples are reported as precisely as possible. Anynumerical values, however, inherently contain certain errors necessarilyresulting from the standard deviation found in their respective testingmeasurements.

It should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between andincluding the recited minimum value of 1 and the recited maximum valueof 10; that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10. Because the disclosednumerical ranges are continuous, they include every value between theminimum and maximum values. Unless expressly indicated otherwise, thevarious numerical ranges specified in this application areapproximations.

All compositional ranges expressed herein are limited in total to and donot exceed 100 percent (volume percent or weight percent) in practice.Where multiple components can be present in a composition, the sum ofthe maximum amounts of each component can exceed 100 percent, with theunderstanding that, and as those skilled in the art readily understand,that the amounts of the components actually used will conform to themaximum of 100 percent.

In order to form a more complete understanding of this disclosure thefollowing terms are defined and should be used with the accompanyingfigures and the description of the various embodiments throughout.

The term “Dilution Index (Y_(d))” and “Dimensionless Modulus (X_(d))”are based on rheological measurements and are fully described in thisdisclosure.

As used herein, the term “monomer” refers to a small molecule that maychemically react and become chemically bonded with itself or othermonomers to form a polymer.

As used herein, the term “α-olefin” is used to describe a monomer havinga linear hydrocarbon chain containing from 3 to 20 carbon atoms having adouble bond at one end of the chain.

As used herein, the terms “ethylene polymer” (and “polyethylene”),refers to macromolecules produced from ethylene monomers and optionallyone or more additional monomers; regardless of the specific catalyst orspecific process used to make the ethylene polymer. In the polyethyleneart, the one or more additional monomers are called “comonomer(s)” andoften include α-olefins. The term “homopolymer” refers to a polymer thatcontains only one type of monomer. Common ethylene polymers include highdensity polyethylene (HDPE), medium density polyethylene (MDPE), linearlow density polyethylene (LLDPE), very low density polyethylene (VLDPE),ultralow density polyethylene (ULDPE), plastomer and elastomers. Theterm ethylene polymer also includes polymers produced in a high pressurepolymerization processes; non-limiting examples include low densitypolyethylene (LDPE), ethylene vinyl acetate copolymers (EVA), ethylenealkyl acrylate copolymers, ethylene acrylic acid copolymers and metalsalts of ethylene acrylic acid (commonly referred to as ionomers). Theterm ethylene polymer also includes block copolymers which may include 2to 4 comonomers. The term ethylene polymer also includes combinationsof, or blends of, the ethylene polymers described above.

The term “linear” ethylene polymer refers to a polymer that is preparedwith a transition metal catalyst—such polymers typically have astructure that is 0predominantly linear whereas ethylene polymersprepared in a high pressure process typically have a large amount oflong chain branching.

The term “heterogeneous ethylene polymer” refers to polymers that areproduced using a heterogeneous catalyst formulation; non-limitingexamples of which include Ziegler-Natta or chromium catalysts.

The term “homogeneous ethylene polymer” refers to polymers that areproduced using metallocene or single-site catalysts. Typically,homogeneous ethylene polymers have narrow molecular weightdistributions, for example gel permeation chromatography (GPC)M_(w)/M_(n) values of less than 2.8; M_(w) and M_(n) refer to weight andnumber average molecular weights, respectively. In contrast, theM_(w)/M_(n) of heterogeneous ethylene polymers are typically, greaterthan the M_(w)/M_(n) of homogeneous ethylene polymers. In general,homogeneous ethylene polymers also have a narrow comonomer distribution,i.e. each macromolecule within the molecular weight distribution has asimilar comonomer content. Frequently, the composition distributionbreadth index “CDBI” is used to quantify how the comonomer isdistributed within an ethylene polymer, as well as to differentiateethylene polymers produced with different catalysts or processes. The“CDBI₅₀” is defined as the percent of ethylene polymer whose compositionis within 50% of the median comonomer composition; this definition isconsistent with that described in U.S. Pat. No. 5,206,075 assigned toExxon Chemical Patents Inc. The CDBI₅₀ of an ethylene polymer can becalculated from TREF curves (Temperature Rising Elution Fractionation);the TREF method is described in Wild et al., J. Polym. Sci., Part B,Polym. Phys., Vol. 20 (3), pages 441-455. Typically the CDBI₅₀ ofhomogeneous ethylene polymers are greater than about 70%. In contrast,the CDBI₅₀ of α-olefin containing heterogeneous ethylene polymers aregenerally lower than the CDBI₅₀ of homogeneous ethylene polymers.

It is well known to those skilled in the art, that homogeneous ethylenepolymers are frequently further subdivided into “linear homogeneousethylene polymers” and “substantially linear homogeneous ethylenepolymers”. These two subgroups differ in the amount of long chainbranching; more specifically, linear homogeneous ethylene polymers haveless than about 0.01 long chain branches per 1000 carbon atoms; whilesubstantially linear ethylene polymers have greater than about 0.01 toabout 3.0 long chain branches per 1000 carbon atoms. A long chain branchis macromolecular in nature, i.e. similar in length to the macromoleculethat the long chain branch is attached to. Hereafter, in thisdisclosure, the term “homogeneous ethylene polymer” refers to bothlinear homogeneous ethylene polymers and substantially linearhomogeneous ethylene polymers.

Herein, the term “polyolefin” includes ethylene polymers and propylenepolymers; non-limiting examples of propylene polymers include isotactic,syndiotactic and atactic propylene homopolymers, random propylenecopolymers containing at least one comonomer and impact polypropylenecopolymers or heterophasic polypropylene copolymers.

The term “thermoplastic” refers to a polymer that becomes liquid whenheated, will flow under pressure and solidify when cooled. Thermoplasticpolymers include ethylene polymers as well as other polymers commonlyused in the plastic industry; non-limiting examples of other polymerscommonly used in film applications include barrier resins (EVOH), tieresins, polyethylene terephthalate (PET), polyamides and the like. Theamount of EVOH may be from 0.5 to 5 weight % (when used) because amaximum use of 5% allows the film to be recycled in many facilities.

As used herein the term “monolayer film” refers to a film containing asingle layer of one or more thermoplastics and multilayer film refers toa film containing more than one layer.

The films of this invention are multilayer films—i.e. they contain morethan one layer. More specifically, the multilayer films of thisinvention have at least three layers—namely two exterior surface layers(which are commonly referred to by those skilled in the art as “skin”layers) and at least one layer between the skin layers—commonly referredto as a “core” layer or layers (with the entire composition between theskin layers also being referred to as the “core”). For clarity: a ninelayer film would have two exterior surface layers (skin layers) andseven core layers. It is also within the scope of this invention toprepare a multilayer core in which the core layers are made with thesame or different types of polyethylenes. If, for example, all of thecore layers are prepared from the same type of polyethylene, then aperson skilled in the art may sometimes refer to these layers(collectively) as a single layer—for clarity—a film made with seven corelayers in which all core layers are made with the same type ofpolyethylene may sometimes be referred to by skilled persons as beingequivalent to a three layer film.

The multilayer films of this invention may be prepared by coextrusion orlamination and both of these techniques are well known. It is also knownto laminate together two multilayer films that have been prepared bycoextrusion—for example, a coextruded film having three layers may belaminated to a coextruded film having five layers to prepare an eightlayer film.

The multilayer films of this invention must contain one skin layer thatcomprises high density polyethylene and another skin layer that containsa linear low density polyethylene having a dilution index, Yd of greaterthan 0°—these requirements help with the fabrication of sealed packagesthat are made from the film. The seals may be formed by applying aheated sealing bar to the skin layer that contains the high densitypolyethylene. Heat from the sealing bar is conducted through thethickness of the film and causes the skin layer that is made with linearlow density polyethylene (which skin layer is commonly referred to assealant layer) to melt, thereby allowing the formation of a seal afterthe source of heat is removed and this layer freezes.

The term “polymeric material” refers to the polymers used to prepare thefilms. A film made from 95 weight % polyethylene and 5 weight % EVOH canbe described as containing 95% by weight polyethylene based on the totalweight of polymeric material used to make the film (i.e. 95÷95+5).

As used herein, the terms “hydrocarbyl”, “hydrocarbyl radical” or“hydrocarbyl group” refers to linear or cyclic, aliphatic, olefinic,acetylenic and aryl (aromatic) radicals comprising hydrogen and carbonthat are deficient by one hydrogen.

As used herein, an “alkyl radical” includes linear, branched and cyclicparaffin radicals that are deficient by one hydrogen radical;non-limiting examples include methyl (—CH₃) and ethyl (—CH₂CH₃)radicals. The term “alkenyl radical” refers to linear, branched andcyclic hydrocarbons containing at least one carbon-carbon double bondthat is deficient by one hydrogen radical.

As used herein, the term “aryl” group includes phenyl, naphthyl, pyridyland other radicals whose molecules have an aromatic ring structure;non-limiting examples include naphthylene, phenanthrene and anthracene.An “arylalkyl” group is an alkyl group having an aryl group pendantthere from; non-limiting examples include benzyl, phenethyl andtolylmethyl; an “alkylaryl” is an aryl group having one or more alkylgroups pendant there from; non-limiting examples include tolyl, xylyl,mesityl and cumyl.

As used herein, the phrase “heteroatom” includes any atom other thancarbon and hydrogen that can be bound to carbon. A“heteroatom-containing group” is a hydrocarbon radical that contains aheteroatom and may contain one or more of the same or differentheteroatoms. In one embodiment, a heteroatom-containing group is ahydrocarbyl group containing from 1 to 3 atoms selected from the groupconsisting of boron, aluminum, silicon, germanium, nitrogen,phosphorous, oxygen and sulfur. Non-limiting examples ofheteroatom-containing groups include radicals of imines, amines, oxides,phosphines, ethers, ketones, oxoazolines heterocyclics, oxazolines,thioethers, and the like. The term “heterocyclic” refers to ring systemshaving a carbon backbone that comprise from 1 to 3 atoms selected fromthe group consisting of boron, aluminum, silicon, germanium, nitrogen,phosphorous, oxygen and sulfur.

As used herein the term “unsubstituted” means that hydrogen radicals arebounded to the molecular group that follows the term unsubstituted. Theterm “substituted” means that the group following this term possessesone or more moieties that have replaced one or more hydrogen radicals inany position within the group; non-limiting examples of moieties includehalogen radicals (F, Cl, Br), hydroxyl groups, carbonyl groups, carboxylgroups, amine groups, phosphine groups, alkoxy groups, phenyl groups,naphthyl groups, C₁ to C₁₀ alkyl groups, C₂ to C₁₀ alkenyl groups, andcombinations thereof. Non-limiting examples of substituted alkyls andaryls include: acyl radicals, alkylamino radicals, alkoxy radicals,aryloxy radicals, alkylthio radicals, dialkylamino radicals,alkoxycarbonyl radicals, aryloxycarbonyl radicals, carbomoyl radicals,alkyl- and dialkyl-carbamoyl radicals, acyloxy radicals, acylaminoradicals, arylamino radicals and combinations thereof.

Herein the term “R1” and its superscript form ^(“R1”) refers to a firstreactor in a continuous solution polymerization process; it beingunderstood that R1 is distinctly different from the symbol R¹; thelatter is used in chemical formula, e.g. representing a hydrocarbylgroup. Similarly, the term “R2” and it's superscript form ^(“R2”) refersto a second reactor, and; the term “R3” and it's superscript form^(“R3”) refers to a third reactor.

As used herein, the term “oligomers” refers to an ethylene polymer oflow molecular weight, e.g., an ethylene polymer with a weight averagemolecular weight (Mw) of about 2,000 to 3,000 daltons. Other commonlyused terms for oligomers include “wax” or “grease”.

Disclosed herein are ethylene polymers having a density of from 0.90 to0.92 and a Dilution Index, yd, of greater than 0. Such polymers may beprepared using known methods, for example the method using a single sitecatalyst and a heterogeneous catalyst as disclosed in U.S. Pat. No.9,512,282.

Single Site Catalyst Formulation

The catalyst components which make up the single site catalystformulation are not particularly limited, i.e. a wide variety ofcatalyst components can be used. One non-limiting embodiment of a singlesite catalyst formulation comprises the following three or fourcomponents: a bulky ligand-metal complex; an alumoxane co-catalyst; anionic activator and optionally a hindered phenol. In Tables 1A, 2A, 3Aand 4A of this disclosure: “(i)” refers to the amount of “component(i)”, i.e. the bulky ligand-metal complex added to R1; “(ii)” refers to“component (ii)”, i.e. the alumoxane co-catalyst; “(iii)” refers to“component (iii)” i.e. the ionic activator, and; “(iv)” refers to“component (iv)”, i.e. the optional hindered phenol.

Non-limiting examples of component (i) are represented by formula (I):

(L^(A))_(a)M(PI)_(b)(Q)_(n)   (I)

wherein (L^(A)) represents a bulky ligand; M represents a metal atom; PIrepresents a phosphinimine ligand; Q represents a leaving group; a is 0or 1; b is 1 or 2; (a+b)=2; n is 1 or 2, and; the sum of (a+b+n) equalsthe valance of the metal M.

Non-limiting examples of the bulky ligand L^(A) in formula (I) includeunsubstituted or substituted cyclopentadienyl ligands orcyclopentadienyl-type ligands, heteroatom substituted and/or heteroatomcontaining cyclopentadienyl-type ligands. Additional non-limitingexamples include, cyclopentaphenanthreneyl ligands, unsubstituted orsubstituted indenyl ligands, benzindenyl ligands, unsubstituted orsubstituted fluorenyl ligands, octahydrofluorenyl ligands,cyclooctatetraendiyl ligands, cyclopentacyclododecene ligands, azenylligands, azulene ligands, pentalene ligands, phosphoyl ligands,phosphinimine, pyrrolyl ligands, pyrozolyl ligands, carbazolyl ligands,borabenzene ligands and the like, including hydrogenated versionsthereof, for example tetrahydroindenyl ligands. In other embodiments,L^(A) may be any other ligand structure capable of η-bonding to themetal M, such embodiments include both η³-bonding and η⁵-bonding to themetal M. In other embodiments, L^(A) may comprise one or moreheteroatoms, for example, nitrogen, silicon, boron, germanium, sulfurand phosphorous, in combination with carbon atoms to form an open,acyclic, or a fused ring, or ring system, for example, aheterocyclopentadienyl ancillary ligand. Other non-limiting embodimentsfor L^(A) include bulky amides, phosphides, alkoxides, aryloxides,imides, carbolides, borollides, porphyrins, phthalocyanines, corrins andother polyazomacrocycles.

Non-limiting examples of metal M in formula (I) include Group 4 metals,titanium, zirconium and hafnium.

The phosphinimine ligand, PI, is defined by formula (II):

(R^(p))₃P═N—  (II)

wherein the R^(p) groups are independently selected from: a hydrogenatom; a halogen atom; C₁₋₂₀ hydrocarbyl radicals which are unsubstitutedor substituted with one or more halogen atom(s); a C₁₋₈ alkoxy radical;a C₆₋₁₀ aryl radical; a C₆₋₁₀ aryloxy radical; an amido radical; a silylradical of formula —Si(R^(S))₃, wherein the R^(S) groups areindependently selected from, a hydrogen atom, a C₁₋₈ alkyl or alkoxyradical, a C₆₋₁₀ aryl radical, a C₆₋₁₀ aryloxy radical, or a germanylradical of formula —Ge(R^(G))₃, wherein the R^(G) groups are defined asR^(S) is defined in this paragraph.

The leaving group Q is any ligand that can be abstracted from formula(I) forming a catalyst species capable of polymerizing one or moreolefin(s). An equivalent term for Q is an “activatable ligand”, i.e.equivalent to the term “leaving group”. In some embodiments, Q is amonoanionic labile ligand having a sigma bond to M. Depending on theoxidation state of the metal, the value for n is 1 or 2 such thatformula (I) represents a neutral bulky ligand-metal complex.Non-limiting examples of Q ligands include a hydrogen atom, halogens,C₁₋₂₀ hydrocarbyl radicals, C₁₋₂₀ alkoxy radicals, C₅₋₁₀ aryl oxideradicals; these radicals may be linear, branched or cyclic or furthersubstituted by halogen atoms, C₁₋₁₀ alkyl radicals, C₁₋₁₀ alkoxyradicals, C₆₋₁₀ arly or aryloxy radicals. Further non-limiting examplesof Q ligands include weak bases such as amines, phosphines, ethers,carboxylates, dienes, hydrocarbyl radicals having from 1 to 20 carbonatoms. In another embodiment, two Q ligands may form part of a fusedring or ring system.

Further embodiments of component (i) of the single site catalystformulation include structural, optical or enantiomeric isomers (mesoand racemic isomers) and mixtures thereof of the bulky ligand-metalcomplexes described in formula (I) above.

The second single site catalyst component, component (ii), is analumoxane co-catalyst that activates component (i) to a cationiccomplex. An equivalent term for “alumoxane” is “aluminoxane”; althoughthe exact structure of this co-catalyst is uncertain, subject matterexperts generally agree that it is an oligomeric species that containrepeating units of the general formula (III):

(R)₂AlO—(Al(R)—O)_(n)—Al(R)₂   (III)

where the R groups may be the same or different linear, branched orcyclic hydrocarbyl radicals containing 1 to 20 carbon atoms and n isfrom 0 to about 50. A non-limiting example of an alumoxane is methylaluminoxane (or MAO) wherein each R group in formula (III) is a methylradical.

The third catalyst component (iii) of the single site catalyst formationis an ionic activator. In general, ionic activators are comprised of acation and a bulky anion; wherein the latter is substantiallynon-coordinating. Non-limiting examples of ionic activators are boronionic activators that are four coordinate with four ligands bonded tothe boron atom. Non-limiting examples of boron ionic activators includethe following formulas (IV) and (V) shown below:

[R⁵]⁺[B(R⁷)₄]⁻  (IV)

where B represents a boron atom, R⁵ is an aromatic hydrocarbyl (e.g.triphenyl methyl cation) and each R⁷ is independently selected fromphenyl radicals which are unsubstituted or substituted with from 3 to 5substituents selected from fluorine atoms, C₁₋₄ alkyl or alkoxy radicalswhich are unsubstituted or substituted by fluorine atoms; and a silylradical of formula —Si(R⁹)₃, where each R⁹ is independently selectedfrom hydrogen atoms and C₁₋₄ alkyl radicals, and; compounds of formula(V):

[(R⁸)_(t)ZH]⁺[B(R⁷)₄]⁻  (V)

where B is a boron atom, H is a hydrogen atom, Z is a nitrogen orphosphorus atom, t is 2 or 3 and R⁸ is selected from C₁₋₈ alkylradicals, phenyl radicals which are unsubstituted or substituted by upto three C₁₋₄ alkyl radicals, or one R⁸ taken together with the nitrogenatom may form an anilinium radical and R⁷ is as defined above in formula(IV).

In both formula (IV) and (V), a non-limiting example of R⁷ is apentafluorophenyl radical. In general, boron ionic activators may bedescribed as salts of tetra(perfluorophenyl) boron; non-limitingexamples include anilinium, carbonium, oxonium, phosphonium andsulfonium salts of tetra(perfluorophenyl)boron with anilinium and trityl(or triphenylmethylium). Additional non-limiting examples of ionicactivators include: triethylammonium tetra(phenyl)boron,tripropylammonium tetra(phenyl)boron, tri(n-butyl)ammoniumtetra(phenyl)boron, trimethylammonium tetra(p-tolyl)boron,trimethylammonium tetra(o-tolyl)boron, tributylammoniumtetra(pentafluorophenyl)boron, tripropylammoniumtetra(o,p-dimethylphenyl)boron, tributylammoniumtetra(m,m-dimethylphenyl)boron, tributylammoniumtetra(p-trifluoromethylphenyl)boron, tributylammoniumtetra(pentafluorophenyl)boron, tri(n-butyl)ammonium tetra(o-tolyl)boron,N,N-dimethylanilinium tetra(phenyl)boron, N,N-diethylaniliniumtetra(phenyl)boron, N,N-diethylanilinium tetra(phenyl)n-butylboron,N,N-2,4,6-pentamethylanilinium tetra(phenyl)boron,di-(isopropyl)ammonium tetra(pentafluorophenyl)boron,dicyclohexylammonium tetra(phenyl)boron, triphenylphosphoniumtetra(phenyl)boron, tri(methylphenyl)phosphonium tetra(phenyl)boron,tri(dimethylphenyl)phosphonium tetra(phenyl)boron, tropilliumtetrakispentafluorophenyl borate, triphenylmethyliumtetrakispentafluorophenyl borate,benzene(diazonium)tetrakispentafluorophenyl borate, tropilliumtetrakis(2,3,5,6-tetrafluorophenyl)borate, triphenylmethyliumtetrakis(2,3,5,6-tetrafluorophenyl)borate, benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)borate, tropillium tetrakis(3,4,5-trifluorophenyl)borate, benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)borate, tropilliumtetrakis(1,2,2-trifluoroethenyl)borate, triphenylmethyliumtetrakis(1,2,2-trifluoroethenyl)borate, benzene(diazonium)tetrakis(1,2,2-trifluoroethenyl)borate, tropilliumtetrakis(2,3,4,5-tetrafluorophenyl)borate, triphenylmethyliumtetrakis(2,3,4,5-tetrafluorophenyl)borate, and benzene(diazonium)tetrakis(2,3,4,5 tetrafluorophenyl)borate. Readily available commercialionic activators include N,N-dimethylanilinium tetrakispentafluorophenylborate, and triphenylmethylium tetrakispentafluorophenyl borate.

The optional fourth catalyst component of the single site catalystformation is a hindered phenol, component (iv). Non-limiting example ofhindered phenols include butylated phenolic antioxidants, butylatedhydroxytoluene, 2,4-di-tertiarybutyl-6-ethyl phenol, 4,4′-methylenebis(2,6-di-tertiary-butylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene andoctadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl) propionate.

To produce an active single site catalyst formulation the quantity andmole ratios of the three or four components, (i) through (iv) areoptimized as described below.

Heterogeneous Catalyst Formulations

A number of heterogeneous catalyst formulations are well known to thoseskilled in the art, including, as non-limiting examples, Ziegler-Nattaand chromium catalyst formulations.

In this disclosure, embodiments include an in-line Ziegler-Nattacatalyst formulation and a batch Ziegler-Natta catalyst formation. Theterm “in-line Ziegler-Natta catalyst formulation” refers to thecontinuous synthesis of a small quantity of active Ziegler-Nattacatalyst and immediately injecting this catalyst into at least onecontinuously operating reactor, wherein the catalyst polymerizesethylene and one or more optional α-olefins to form an ethylene polymer.The terms “batch Ziegler-Natta catalyst formulation” or “batchZiegler-Natta procatalyst” refer to the synthesis of a much largerquantity of catalyst or procatalyst in one or more mixing vessels thatare external to, or isolated from, the continuously operating solutionpolymerization process. Once prepared, the batch Ziegler-Natta catalystformulation, or batch Ziegler-Natta procatalyst, is transferred to acatalyst storage tank. The term “procatalyst” refers to an inactivecatalyst formulation (inactive with respect to ethylene polymerization);the procatalyst is converted into an active catalyst by adding an alkylaluminum co-catalyst. As needed, the procatalyst is pumped from thestorage tank to at least one continuously operating reactor, where anactive catalyst is formed and polymerizes ethylene and one or moreoptional α-olefins to form an ethylene polymer. The procatalyst may beconverted into an active catalyst in the reactor or external to thereactor.

A wide variety of chemical compounds can be used to synthesize an activeZiegler-Natta catalyst formulation. The following describes variouschemical compounds that may be combined to produce an activeZiegler-Natta catalyst formulation. Those skilled in the art willunderstand that the embodiments in this disclosure are not limited tothe specific chemical compound disclosed.

An active Ziegler-Natta catalyst formulation may be formed from: amagnesium compound, a chloride compound, a metal compound, an alkylaluminum co-catalyst and an aluminum alkyl. In Table 1A, 2A, 3A and 4Aof this disclosure: “(v)” refers to “component (v)” the magnesiumcompound; the term “(vi)” refers to the “component (vi)” the chloridecompound; “(vii)” refers to “component (vii)” the metal compound;“(viii)” refers to “component (viii)” alkyl aluminum co-catalyst, and;“(ix)” refers to “component (ix)” the aluminum alkyl. As will beappreciated by those skilled in the art, Ziegler-Natta catalystformulations may contain additional components; a non-limiting exampleof an additional component is an electron donor, e.g. amines or ethers.

A non-limiting example of an active in-line Ziegler-Natta catalystformulation can be prepared as follows. In the first step, a solution ofa magnesium compound (component (v)) is reacted with a solution of thechloride compound (component (vi)) to form a magnesium chloride supportsuspended in solution. Non-limiting examples of magnesium compoundsinclude Mg(R¹)₂; wherein the R¹ groups may be the same or different,linear, branched or cyclic hydrocarbyl radicals containing 1 to 10carbon atoms. Non-limiting examples of chloride compounds include R²Cl;wherein R² represents a hydrogen atom, or a linear, branched or cyclichydrocarbyl radical containing 1 to 10 carbon atoms. In the first step,the solution of magnesium compound may also contain an aluminum alkyl(component (ix)). Non-limiting examples of aluminum alkyl includeAl(R³)₃, wherein the R³ groups may be the same or different, linear,branched or cyclic hydrocarbyl radicals containing from 1 to 10 carbonatoms. In the second step a solution of the metal compound (component(vii)) is added to the solution of magnesium chloride and the metalcompound is supported on the magnesium chloride. Non-limiting examplesof suitable metal compounds include M(X)_(n) or MO(X)_(n); where Mrepresents a metal selected from Group 4 through Group 8 of the PeriodicTable, or mixtures of metals selected from Group 4 through Group 8; Orepresents oxygen, and; X represents chloride or bromide; n is aninteger from 3 to 6 that satisfies the oxidation state of the metal.Additional non-limiting examples of suitable metal compounds includeGroup 4 to Group 8 metal alkyls, metal alkoxides (which, may be preparedby reacting a metal alkyl with an alcohol) and mixed-ligand metalcompounds that contain a mixture of halide, alkyl and alkoxide ligands.In the third step a solution of an alkyl aluminum co-catalyst (component(viii)) is added to the metal compound supported on the magnesiumchloride. A wide variety of alkyl aluminum co-catalysts are suitable, asexpressed by formula (VI):

Al(R⁴)_(p)(OR⁵)_(q)(X)_(r)   (VI)

wherein the R⁴ groups may be the same or different, hydrocarbyl groupshaving from 1 to 10 carbon atoms; the OR⁵ groups may be the same ordifferent, alkoxy or aryloxy groups wherein R⁵ is a hydrocarbyl grouphaving from 1 to 10 carbon atoms bonded to oxygen; X is chloride orbromide, and; (p+q+r)=3, with the proviso that p is greater than 0.Non-limiting examples of commonly used alkyl aluminum co-catalystsinclude trimethyl aluminum, triethyl aluminum, tributyl aluminum,dimethyl aluminum methoxide, diethyl aluminum ethoxide, dibutyl aluminumbutoxide, dimethyl aluminum chloride or bromide, diethyl aluminumchloride or bromide, dibutyl aluminum chloride or bromide and ethylaluminum dichloride or dibromide.

The process described in the paragraph above, to synthesize an activein-line Ziegler-Natta catalyst formulation, can be carried out in avariety of solvents; non-limiting examples of solvents include linear orbranched C₅ to C₁₂ alkanes or mixtures thereof. To produce an activein-line Ziegler-Natta catalyst formulation the quantity and mole ratiosof the five components, (v) through (ix), are optimized as describedbelow.

Additional embodiments of heterogeneous catalyst formulations includeformulations where the “metal compound” is a chromium compound;non-limiting examples include silyl chromate, chromium oxide andchromocene. In some embodiments, the chromium compound is supported on ametal oxide such as silica or alumina. Heterogeneous catalystformulations containing chromium may also include co-catalysts;non-limiting examples of co-catalysts include trialkylaluminum,alkylaluminoxane and dialkoxyalkylaluminum compounds and the like.

Ethylene polymers having a dilution index of greater than 0° may beproduced using the above described two catalyst systems (single site andheterogenous) in a polymerization process, especially the solutionpolymerization process described in U.S. Pat. No. 9,152,282.

Dilution Index (Y_(d)) and Dimensionless Modulus (Xd)

Dilution Index (Y_(d), having dimensions of ° (degrees)) andDimensionless Modulus (X_(d)) may be used to describe polyethylenes.Polyethylene may be categorized by Yd and Xd as follows:

-   -   Type I: Y_(d)>0 and X_(d)<0;    -   Type II: Y_(d)>0 and X_(d)>0; and    -   Type III: Y_(d)<0 and X_(d)>0.

Further detail about these types is found in U.S. Pat. No. 9,512,282.The polyethylene used in the sealant layer of the films disclosed hereincan be prepared with a dual catalyst system (a single site catalyst anda heterogenous catalyst), and has a Dilution Index, Yd of greater than0°. However, comparative (and commercially available) polyethylenes suchas ELITE® 5100G and ELITE® 5400G (both ethylene/1-octene polymersavailable from The Dow Chemical Company (Midland, Mich., USA)) are alsobelieved to be prepared with a similar dual catalyst system but have aDilution Index of less than 0° and are not suitable for in thecompositions described herein.

Further description of Dilution Index (Y_(d)) and Dimensionless Modulus(X_(d)) follows. In addition to having molecular weights, molecularweight distributions and branching structures, blends of ethylenepolymers may exhibit a hierarchical structure in the melt phase. Inother words, the ethylene polymer components may be, or may not be,homogeneous down to the molecular level depending on polymer miscibilityand the physical history of the blend. Such hierarchical physicalstructure in the melt is expected to have a strong impact on flow andhence on processing and converting; as well as the end-use properties ofmanufactured articles. The nature of this hierarchical physicalstructure between polymers can be characterized.

The hierarchical physical structure of ethylene polymers can becharacterized using melt rheology. A convenient method can be based onthe small amplitude frequency sweep tests. Such rheology results areexpressed as the phase angle δ as a function of complex modulus G*,referred to as van Gurp-Palmen plots (as described in M. Van Gurp, J.Palmen, Rheol. Bull. (1998) 67(1): 5-8, and; Dealy J, Plazek D. Rheol.Bull. (2009) 78(2): 16-31). For a typical ethylene polymer, the phaseangle δ increases toward its upper bound of 90° with G* becomingsufficiently low. A typical VGP plot is shown in FIG. 4. The VGP plotsare a signature of resin architecture. The rise of δ toward 90° ismonotonic for an ideally linear, monodisperse polymer. The δ (G*) for abranched polymer or a blend containing a branched polymer may show aninflection point that reflects the topology of the branched polymer (seeS. Trinkle, P. Walter, C. Friedrich, Rheo. Acta (2002) 41: 103-113). Thedeviation of the phase angle δ from the monotonic rise may indicate adeviation from the ideal linear polymer either due to presence of longchain branching if the inflection point is low (e.g. ‘δ’≤20°) or a blendcontaining at least two polymers having dissimilar branching structureif the inflection point is high (e.g. δ≥70°).

For commercially available linear low density polyethylenes, inflectionpoints are not observed; with the exception of some commercialpolyethylenes that contain a small amount of long chain branching (LCB).To use the VGP plots regardless of presence of LCB, an alternative is touse the point where the frequency ω_(c) is two decades below thecross-over frequency ω_(c), i.e., ω_(c)=0.010ω_(x). The cross-over pointis taken as the reference as it is known to be a characteristic pointthat correlates with MI, density and other specifications of an ethylenepolymer. The cross-over modulus is related to the plateau modulus for agiven molecular weight distribution (see S. Wu. J Polym Sci, Polym PhysEd (1989) 27:723; M. R. Nobile, F. Cocchini. Rheol Acta (2001) 40:111).The two decade shift in phase angle δ is to find the comparable pointswhere the individual viscoelastic responses of constituents could bedetected; to be more clear, this two decade shift is shown in FIG. 5.The complex modulus G*_(c) for this point is normalized to thecross-over modulus, G*_(x)/(√{square root over (2)}), as (√{square rootover (2)})G*_(c)/G*_(x), to minimize the variation due to overallmolecular weight, molecular weight distribution and the short chainbranching. As a result, the coordinates on VGP plots for this lowfrequency point at ω_(c)=0.010ω_(x), namely (√{square root over(2)})G*_(c)/G*_(x) and δ_(c), characterize the contribution due toblending. Similar to the inflection points, the closer the ((√{squareroot over (2)})G*_(c)/G*_(x), δ_(c)) point is toward the 90° upperbound, the more the blend behaves as if it were an ideal singlecomponent.

As an alternative way to avoid interference due to the molecular weight,molecular weight distribution and the short branching of the ethyleneδ_(c) polymer ingredients, the coordinates (G*_(c), δ_(c)) are comparedto a reference sample of interest to form the following two parameters:

-   -   “Dilution Index (Y_(d))”

Y _(d)=δ_(c)−(C ₀ −C ₁ e ^(C) ² ^(ln G*) ^(c) ⁾

-   -   “Dimensionless Modulus (X_(d))”

X _(d)=log(G* _(c) /G* _(r))

The constants C₀, C₁, and C₂ are determined by fitting the VGP dataδ(G*) of the reference sample to the following equation:

δ=C ₀ −C ₁ e ^(C) ² ^(ln G*)

G*_(r) is the complex modulus of this reference sample at itsδ_(c)=δ(0.01ω_(x)). When an ethylene polymer, synthesized with anin-line Ziegler-Natta catalyst employing one solution reactor, having adensity of 0.920 g/cm³ and a melt index (MI or I₂) of 1.0 dg/min istaken as a reference sample, the constants are:

-   -   C₀=93.43°    -   C₁=1.316°    -   C₂=0.2945    -   G*_(r)=9432 Pa.

The values of these constants can be different if the rheology testprotocol differs from that specified herein.

These regrouped coordinates (X_(d), Y_(d)) from (G*_(c), δ_(c)) allowscomparison between ethylene polymer products disclosed herein withComparative examples. The Dilution Index (Y_(d)) reflects whether theblend behaves like a simple blend of linear ethylene polymers (lackinghierarchical structure in the melt) or shows a distinctive response thatreflects a hierarchical physical structure within the melt. The lowerthe Y_(d), the more the sample shows separate responses from theethylene polymers that comprise the blend; the higher the Y_(d) the morethe sample behaves like a single component, or single ethylene polymer.

A solution polymerization process that uses two catalysts enables themanufacture of ethylene polymer products having higher X_(d). Notwishing to be bound by theory, as X_(d) increases the macromolecularcoils of higher molecular weight fraction are more expanded and uponcrystallization the probability of tie chain formation is increasedresulting in higher toughness properties: the polyethylene art isreplete with disclosures that correlate higher toughness (such as higherdart impact in film applications) with an increasing probability of tiechain formation.

In the Dilution Index testing protocol, the upper limit on Y_(d) of thepolyethylene used to prepare the sealant skin layer may be about 20, insome cases about 15 and is other cases about 13. The lower limit onY_(d) may be about −30, in some cases −25, in other cases −20 and instill other cases −15.

In the Dilution Index testing protocol, the upper limit on X_(d) is 1.0,in some cases about 0.95 and in other cases about 0.9. The lower limiton X_(d) is −2, in some cases −1.5 and in still other cases −1.0. In anembodiment, the polyethylene used in the sealant skin layer may have aDilution Index of from 0.5 to 10, especially from 1 to 5°.

Terminal Vinyl Unsaturation of Ethylene Polymer Products

Polyethylene may be further characterized by terminal vinylunsaturation. Preferred polymers for use in the sealant skin layer ofthe films have such unsaturation in amounts of greater than or equal to0.03 terminal vinyl groups per 100 carbon atoms (≥0.03 terminalvinyls/100 C); as determined via Fourier Transform Infrared (FTIR)spectroscopy according to ASTM D3124-98 and ASTM D6248-98. In anembodiment, the polyethylene used to prepare the sealant skin layer hasfrom 0.04 to 0.06 terminal vinyls/100 C.

Catalyst Residues (Total Catalytic Metal)

The polyethylene used in the sealant skin layer will typically alsocontain greater than 3 parts per million (ppm) of at least one Group IVtransition metal (especially Ti) where the quantity of catalytic metalwas determined by Neutron Activation Analysis (N.A.A.) as specifiedherein. In contrast, most commercially available single site catalyzedpolyethylene contains less than 3 ppm of Group IV metal i.e. thepolyethylene that is produced using only a single site catalysttypically contains less titanium residue than the “DC” polymersdisclosed herein.

Additives and Adjuvants

The ethylene polymers used herein may optionally include, depending onits intended use, additives and adjuvants. Non-limiting examples ofadditives and adjuvants include, anti-blocking agents, antioxidants,heat stabilizers, slip agents, processing aids, anti-static additives,colorants, dyes, filler materials, light stabilizers, heat stabilizers,light absorbers, lubricants, pigments, plasticizers, nucleating agentsand combinations thereof. Non-limiting examples of suitable primaryantioxidants include IRGANOX® 1010 [CAS Reg. No. 6683-19-8] and IRGANOX®1076 [CAS Reg. No. 2082-79-3]; both available from BASF Corporation,Florham Park, N.J., U.S.A. Non-limiting examples of suitable secondaryantioxidants include IRGAFOS® 168 [CAS Reg. No. 31570-04-4], availablefrom BASF Corporation, Florham Park, N.J., U.S.A.; Weston 705 [CAS Reg.No. 939402-02-5], available from Addivant, Danbury Conn., U.S.A. and;DOVERPHOS® IGP-11 [CAS Reg. No. 1227937-46-3] available form DoverChemical Corporation, Dover Ohio, U.S.A.

Testing Methods Density

Polyethylene densities are determined using ASTM D792-13 (Nov. 1, 2013).

Melt Index

Polyethylene melt index measurements is determined using ASTM D1238(Aug. 1, 2013). Melt indexes, I₂, I₆, I₁₀ and I₂₁ were measured at 190°C., using weights of 2.16 kg, 6.48 kg, 10 kg and a 21.6 kg respectively.Melt index is commonly report with units of g/10 minute or dg/minute;these units are equivalent. Herein, the term “stress exponent” or itsacronym “S.Ex.”, is defined by the following relationship:

S. Ex.=log(I₆/I₂)/log(6480/2160)

wherein I₆ and I₂ are the melt flow rates measured at 190° C. using 6.48kg and 2.16 kg loads, respectively. In this disclosure, melt index isexpressed using the units of g/10 minute or g/10 min or dg/minute ordg/min; these units are equivalent.

Gel Permeation Chromatography (GPC)

Polyethylene molecular weights, M_(n), M_(w) and M_(z), as well the asthe polydispersity (M_(w)/M_(n)), are determined using ASTM D6474-12(Dec. 15, 2012). This method illuminates the molecular weightdistributions of ethylene polymer products by high temperature gelpermeation chromatography (GPC). The method uses commercially availablepolystyrene standards to calibrate the GPC.

Unsaturation Content

The quantity of unsaturated groups, i.e. double bonds, in a polyethyleneproduct is determined according to ASTM D3124-98 (vinylideneunsaturation, published March 2011) and ASTM D6248-98 (vinyl and transunsaturation, published July 2012).

Comonomer Content

The quantity of comonomer in polyethylene is determined by FTIR (FourierTransform Infrared spectroscopy) according to ASTM D6645-01 (publishedJanuary 2010).

Composition Distribution Branching Index (CDBI)

The “Composition Distribution Branching Index” or “CDBI” is determinedusing a crystal-TREF unit commercially available form Polymer Char(Valencia, Spain). The acronym “TREF” refers to Temperature RisingElution Fractionation. A sample of polyethylene (80 to 100 mg) is placedin the reactor of the Polymer Char crystal-TREF unit, the reactor isfilled with 35 ml of 1,2,4-trichlorobenzene (TCB), heated to 150° C. andheld at this temperature for 2 hours to dissolve the sample.

An aliquot of the TCB solution (1.5 mL) is then loaded into the PolymerChar TREF column filled with stainless steel beads and the column isequilibrated for 45 minutes at 110° C. The polyethylene is thencrystallized from the TCB solution, in the TREF column, by slowlycooling the column from 110° C. to 30° C. using a cooling rate of 0.09°C. per minute. The TREF column is then equilibrated at 30° C. for 30minutes. The crystallized polyethylene is then eluted from the TREFcolumn by passing pure TCB solvent through the column at a flow rate of0.75 mL/minute as the temperature of the column is slowly increased from30° C. to 120° C. using a heating rate of 0.25° C. per minute. UsingPolymer Char software a TREF distribution curve is generated as theethylene polymer product is eluted from the TREF column, i.e. a TREFdistribution curve is a plot of the quantity (or intensity) of ethylenepolymer eluting from the column as a function of TREF elutiontemperature. A CDBI₅₀ is calculated from the TREF distribution curve.The “CDBI₅₀” is defined as the percent of ethylene polymer whosecomposition is within 50% of the median comonomer composition (25% oneach side of the median comonomer composition); it is calculated fromthe TREF composition distribution curve and the normalized cumulativeintegral of the TREF composition distribution curve. Those skilled inthe art will understand that a calibration curve is required to converta TREF elution temperature to comonomer content, i.e. the amount ofcomonomer in the ethylene polymer fraction that elutes at a specifictemperature. The generation of such calibration curves are described in,e.g. Wild et al., J. Polym. Sci., Part B, Polym. Phys., Vol. 20 (3),pages 441-455: hereby fully incorporated by reference.

Neutron Activation Analysis (NAA)

Neutron Activation Analysis, hereafter NAA, is used to determinecatalyst residues in polyethylene and is performed as follows. Aradiation vial (composed of ultrapure polyethylene, 7 mL internalvolume) is filled with a polyethylene sample and the sample weight isrecorded. Using a pneumatic transfer system the sample is placed insidea SLOWPOKE® nuclear reactor (Atomic Energy of Canada Limited, Ottawa,Ontario, Canada) and irradiated for 30 to 600 seconds for shorthalf-life elements (e.g. Ti, V, Al, Mg, and Cl) or 3 to 5 hours for longhalf-life elements (e.g. Zr, Hf, Cr, Fe and Ni). The average thermalneutron flux within the reactor is 5×10¹¹/cm²/s. After irradiation,samples are withdrawn from the reactor and aged, allowing theradioactivity to decay; short half-life elements were aged for 300seconds (or long half-life elements are aged for several days). Afteraging, the gamma-ray spectrum of the sample is recorded using agermanium semiconductor gamma-ray detector (ORTEC® model GEM55185,Advanced Measurement Technology Inc., Oak Ridge, Tenn., USA) and amultichannel analyzer (ORTEC® model DSPEC Pro®). The amount of eachelement in the sample was calculated from the gamma-ray spectrum andrecorded in parts per million relative to the total weight of theethylene polymer sample. The N.A.A. system is calibrated with SPECPURE®standards (1000 ppm solutions of the desired element (greater than 99%pure)). One mL of solutions (elements of interest) is pipetted onto a 15mm×800 mm rectangular paper filter and air dried. The filter paper isthen placed in a 1.4 mL polyethylene irradiation vial and analyzed bythe N.A.A. system. Standards are used to determine the sensitivity ofthe N.A.A. procedure (in counts/μg).

Dilution Index (Y_(d)) Measurements

A series of small amplitude frequency sweep tests were run on eachsample using an Anton Paar MCR501 Rotational Rheometer equipped with the“TruGap™ Parallel Plate measuring system”. A gap of 1.5 mm and a strainamplitude of 10% were used throughout the tests. The frequency sweepswere from 0.05 to 100 rad/s at the intervals of seven points per decade.The test temperatures were 170°, 190°, 210° and 230° C. Master curves at190° C. were constructed for each sample using the Rheoplus/32 V3.40software through the Standard TTS (time-temperature superposition)procedure, with both horizontal and vertical shift enabled.

The flow properties of the polyethylene, e.g., the melt strength andmelt flow ratio (MFR) are well characterized by the Dilution Index(Y_(d)) and the Dimensionless Modulus (X_(d)) as described in U.S. Pat.No. 9,512,282. In both cases, the flow property is a strong function ofY_(d) and X_(d) in addition a dependence on the zero-shear viscosity.For example, the melt strength (hereafter MS) values of thepolyethylenes were found to follow the same equation, confirming thatthe characteristic VGP point ((√{square root over (2)})G*_(c)/G*_(x),δ_(c)) and the derived regrouped coordinates (X_(d), Y_(d)) representthe structure well:

MS=α ₀₀+α₁₀ log η₀−α₂₀(90−δ_(c))−α₃₀((√{square root over (2)})G* _(c)/G* _(x))−α₄₀(90−δ_(c))((√{square root over (2)})G* _(c) /G* _(x))

where

-   -   a₀₀=−33.33; a₁₀=9.529; a₂₀=0.03517; a₃₀=0.894; a₄₀=0.02969        and r²=0.984 and the average relative standard deviation was        0.85%. Further, this relation can be expressed in terms of the        Dilution Index (Y_(d)) and the Dimensionless Modulus (X_(d)):

MS=α ₀+α₁ log η₀+α₂ Y _(d)+α₃ X _(d)+α₄ Y _(d) X _(d)

where

-   -   a₀=33.34; a₁=9.794; a₂=0.02589; a₃=0.1126; a₄=0.03307 and        r²=0.989 and the average relative standard deviation was 0.89%.

The MFR of the polyethylenes disclosed in U.S. Pat. No. 9,512,282 werefound to follow a similar equation, further confirming that the dilutionparameters Y_(d) and X_(d) show that the flow properties of the novelpolyethylenes of U.S. Pat. No. 9,512,282 differ from the reference andcomparative polyethylenes:

MFR=b ₀ −b ₁ log η₀ −b ₂ Y _(d) −b ₃ X _(d)

where

-   -   b₀=53.27; b₁=6.107; b₂=1.384; b₃=20.34        and r²=0.889 and the average relative standard deviation and        3.3%.

EXAMPLES

Other test procedures that are useful for measuring film properties arebriefly described below.

Gloss is determined by ASTM D2457.

Haze is determined by ASTM D1003.

Tensile properties (% elongation and tensile strength at break) weredetermined by ASTM D638.

Film rigidity is measured using a test procedure that is in substantialaccordance with ASTM D2923 (“Rigidity of Polyolefin Film and Sheeting”).The test instrument has a sample platform that contains a linear slot.The sample of the film that is to be tested is placed on the platformand a blade is then used to force the film into the slot. The width ofthe slot is 10 mm. The film sample is 4″×4″ (10.2 cm by 10.2 cm). Theresults from the test are plotted on a load (in grams) versus extension(in cm) graph. The peak load that is observed during the test (in grams)is divided by the length of the sample (10.16 cm) to produce a“rigidity” value (reported in grams per cm). The test is conducted inboth the machine direction (MD) and traverse direction (TD). Rigidityresults may be reported as MD; TD; or the average of MD+TD.

The following materials (polyethylene and EVOH) were used in theexamples (Table 1).

TABLE 1 Material (polyethylene or Melt Index, I₂ Density EVOH) (g/10min) (g/cm³) Comonomer 1 (DC) (1)   0.914 1-octene 2 (Z/N) 1   0.958none 3-t (Z/N) 0.8 0.934 1-hexene 4 EVOH 1.6 1.19 — 5 0.8 0.934 1-hexene6 (SSC) 1.2 0.967 none 7 (DC) 0.9 0.919 1-octene 8 (Z/N) 0.9 0.9121-octene

The term “ZN” in brackets above indicates that the polyethylene wasprepared with a Ziegler Natta catalyst system. The term “SSC” indicatesthat the polyethylene was prepared with a single site catalyst system.The term “DC” indicates that the polyethylene was prepared with a DualCatalyst system that includes a Z/N catalyst and a SSC catalyst.Polyethylene 1 (DC) in Table 1 has a Dilution Index, Yd, of 3.4°; adimensionless modulus of −0.05 and contains about 10 ppm residualtitanium. Polyethylene 1 was prepared in the manner described in U.S.Pat. No. 9,512,282, i.e. using a dual catalyst system (a single sitecatalyst having a titanium-phosphinimine/cyclopentadienyl molecule and aheterogeneous Z/N catalyst).

Polyethylene 6 contains 1200 ppm of a nucleating agent sold under thetrademark HYPERFORM® 20E by Milliken Chemicals. Polyethylene 3-t is ablend of 80 weight % of Polyethylene 5+20 weight % of a “tie” resin(sold under the tradename BYNEL® 41E710 by DuPont and reported to be amaleic anhydride modified polyethylene).

This blend 3-t serves as a “tie layer” to ensure good adhesion of thepolyethylene layers to the ethylene-vinyl-alcohol (EVOH) resin shown asmaterial 4 in Table 1. Polyethylene 1 and Polyethylene 7 were made insubstantial accordance with the process in the examples of U.S. Pat. No.9,512,282. The EVOH shown as material 4 is sold under the tradenameEVAL™ F171B by Kurrary Industries of Japan.

Example: Improved SUP Process

Comparative: Several retail stand up pouches containing foods werepurchased at a grocery store. These SUPs were prepared with aconventional PET/PE structure. Film rigidity testing was carried out ona number of films obtained from these retail packages. The film sampleseach had a thickness of about 3.5 mil. Using the blade/slot apparatusdescribed above, the average rigidity was measured at 5.5 g/cm in boththe MD and TD directions. MD rigidity is important because it affectsthe ability of the SUP to be self-supporting (i.e. to “stand”). It isalso important to provide this rigidity with minimum film thicknessbecause down gauged/thinner films use less material. This PET/PEstructure has a rigidity/thickness ratio of 5.5 g/cm/3.5 mils (i.e. when“normalized” to a thickness of 1 mil, this corresponds to a rigidity of1.6 g/cm per mil of thickness in the MD).

Comparative 2: A 4 layer coextruded film structure was made using ablown film line. The coextruded structure had an overall thickness of3.5 mils and had the architecture shown in Table 2.

TABLE 2 Comparative Film 2 Film Structure Layer Material Type Thickness(mils) (Skin) 1 2 0.75 2 5 0.8 3 6 1.5 (Skin) 4 8 0.45

TABLE 3 Inventive 1 Film Layer Material Type Amount (weight %) (Skin) 11 12.0 2 6 14.0 3 6 14.0 4 6 16.0 5 5 7.0 6 5 8.0 7 5 8.0 8 2 10.0(Skin) 9 2 11.0

The PE types correspond to the descriptions shown in Table 1.

Film rigidity testing was carried out on the structure shown in Table 2and values of 7.9 g/cm in the MD direction and 6.6 g/cm in the TD wereobtained. Thus, the normalized MD rigidity of this coextruded multilayerfilm structure is 7.9/3.5 or 2.3 g/cm per mil of thickness. Thiscompares very well to the normalized MD rigidity of 1.6 g/cm per mil ofthickness that was measured in a PET/PE structure in commercial use inretail packaging.

Inventive Film 1: A nine layer coextruded film structure was made usinga blown film line. The coextruded structure had an overall thickness of3.5 mils and had the composition shown in Table 3. For clarity—skin 1layer is made from Material 1 and is present in an amount of 12 weight%. As shown in Table 1 and accompanying notes, Material 1 is a linearlow density polyethylene having a Dilution Index of 3.4 and a density of0.914 g/cc. This skin layer 1 may also be referred to as the sealantlayer or the sealant skin layer. The second skin layer—layer 9 in Table3—is made from Material 2 and is present in an amount of 11 weight %.Material 2 is a high density polyethylene homopolymer (i.e. nocomonomer) having a density of 0.958 g/cc and is made with a Z/Ncatalyst. The core of inventive film 1 consists of layers 2-8 and ismade from Material 6 (a high density ethylene polymer having a densityof 0.967 g/cc) and Material 5 (a medium density polyethylene having adensity of 0.934 g/cc) in the amounts indicated in Table 3.

“Comparative 2” film structure was used for the preparation of SUPpackages on a conventional “SUP machine” that is purpose-designed forthe conversion of polymeric roll stock into SUP packages. Priorpolymeric roll stock typically consists of a layer of polyester (PET)and a layer of polyethylene (PE).

The PET layer of prior films provides high rigidity. In addition, PEThas a higher melting point than PE and PET has good tensile strength.The SUP machine places an elongational load on the roll stock during theprocess to convert the roll stock to SUP packages. In addition, heat isapplied to the roll stock in order to form the seals of the SUP package.Thus, the roll stock needs to resist the elongational forces (because,if the roll stock is stretched, the printing and cutting of the SUPpackages will be “off center”) and the roll stock needs to form strongseals.

Heat from the sealing bar is applied to the skin layer made from highdensity polyethylene (because it has a higher melting point, and is moreresistant to “burn through” than the low density seal/skin layer). Theseal is formed when two adjacent sealant skin layers melt together.

It will be recognized by those skilled in the art that the melting pointof linear polyethylene is a function of density/comonomer content andthat the melting point generally decreases as density decreases. Thedensity of the sealant layer of comparative 2 reflects this—it has avery low density of 0.912 g/cc.

The roll stock of comparative 2 can be readily converted into SUPpackages on conventional SUP machinery. It is possible to prepare highquality SUP packages (with the printing properly “centered” on thepackages and with strong seals) at high production rates. In general,the production rate can be limited by mis-formed seals.

We have now observed that it is possible to improve SUP packageproduction efficiency with the use of a polyethylene having a DilutionIndex of greater than 0°.

One important difference between comparative 2 and Inventive 1 is thatthe roll stock of Inventive 1 has a sealant skin layer made from apolyethylene having a Dilution Index of greater than 0. It is alsonotable that the density of this resin is 0.914 g/cc (whereas thecomparative skin layer of comparative 2 has a density of 0.912 g/cc)because lower density polyethylene is generally preferred for thepreparation of seals. The roll stock of inventive 1 can also be readilyconverted onto SUP packages on conventional SUP machinery. The use ofthis roll stock can allow higher production rates and/or fewer packagefailures at a given production rate than the use of comparative 2 rollstock. Again, this is surprising because the density of the sealantlayer in inventive 1 is actually higher than the density of the sealantlayer of comparative 2.

The coextruded (or “coex”) films disclosed herein (and demonstrated inexamples 2 and 3) were prepared on a conventional blown film line. Itwill be recognized by those skilled in the art that multilayer films mayalso be prepared by conventional laminator techniques.

Examples 2 and 3

Multilayer Films with Improved Impact Properties

The film labelled inventive 1 in example 1 has one skin layer preparedfrom high density polyethylene and the other skin layer (also referredto as the sealant layer) that is prepared from a linear low densitypolyethylene having a Dilution index of greater than 0°. These filmshave been found to provide excellent processability on SUP conversionmachinery. The core (i.e. interior layers) of inventive 1 were preparedusing high and medium density polyethylene. This provides good rigidity(which is desirable for SUP packages) but the impact strength of thesepackages is not very high.

Examples 2 and 3 illustrate multilayer films having skin layers that usethe skin layers of inventive 1 (i.e. one skin layer is a high densitypolyethylene and the other skin layer is a skin sealant layer made froma linear low density polyethylene having a Dilution Index of greaterthan 0); however, the core of the multilayer films of these examples isprepared using polymers having a lower density (on an overall/averagebasis in comparison to inventive 1).

The films of examples 2 and 3 are not optimized for the preparation ofSUP packages. In comparison to the use of inventive film 1, these filmswould be expected to produce a less rigid/more “floppy” SUPpackage—and—it is probable that these films would not be as“processable” on SUP machinery (which means that these films would beexpected to run at lower production rates on SUP machinery).

However, the films of examples 2 and 3 are suitable for other Form FillSeal (FFS) machines, including Vertical FFS (VFFS) machines. Again, theheat required for forming seals in the FFs packages would be applied tothe high density skin layer. The heat will then be transmitted/conductedthrough the thickness of the film to cause the sealant skin layer tomelt and form a seal. As noted, the sealant skin layer of the films ofthese examples is made with a linear low density polyethylene having aDilution Index of greater than 0—and we have observed that this type ofpolyethylene provides strong seals with a high level of caulkability.

The composition of inventive film structure 2 is described in Table 4.The thickness of the film is 4 mils.

This film was also subjected to a thermal embossing operation that leftcross hatches (i.e. a plurality of small square shapes) in the film. Thefilm withstood the embossing process without suffering “burn through”(where “burn through” means that the film melted and flowed away,leaving holes in the film).

TABLE 4 Inventive Film Structure 2 Layer Material Amount (weight %)(Skin) 1 1 11.0 2 2 9.0 3 2 10.0 4 3-t 14.5 5 4 5.0 6 3-t 14.5 7 5 18.08 2 9.0 (Skin) 9 2 9.0

Fifteen samples of inventive film 2 were measured to determineelongation (%) and tensile strength at break (pounds per square inch,psi) in both the MD and TD direction. The film was determined to have anMD elongation of 642 (standard deviation of 78); and MD tensile at breakof 3977 (standard deviation of 366); a TD elongation of 613 (standarddeviation of 172) and a tensile at break of 3256 (standard deviation of278).

Example 3

The composition of inventive film 3 is shown in Table 5. The thicknessof the film is 4 mils.

This film was also subjected to a thermal embossing operation withoutsuffering “burn through.”

TABLE 5 Inventive Film 3 Structure Layer Material Amount (weight %)(Skin) 1 1 11.0 2 6 6.0 3 6 6.0 4 7 16.0 5 6 5.0 6 7 14.5 7 7 18.0 8 713.5 (Skin) 9 2 10.0

Example 3 Film Properties

The dart impact strength of Inventive film 3 was measured as 2,398grams. The machine direction (MD) tensile strength was 6335 psi. Thetraverse direction (TD) tensile strength was 6629 psi. The MD elongationof film 3 was 1052%. The TD elongation was 998%

INDUSTRIAL APPLICABILITY

Multilayer films having improved sealing properties are disclosed. Thefilms are suitable for a wide variety of flexible packagingapplications, including the production of Stand Up Pouch packages.

1-5. (canceled)
 6. A process to make a sealed package with a multilayerfilm comprising: a first skin layer consisting of from 85 to 100 weight% of a high density polyethylene having a density of from 0.95 to 0.97g/cc and a melt index, I₂, of from 0.5 to 10 g/10 minutes; a second skinlayer consisting of from 85 to 100 weight % of a first linear lowdensity interpolymer having a molecular weight distribution M_(w)/M_(n)of from 2.5 to 4.0, a density of from 0.90 to 0.92 g/cc, a melt index,I₂, of from 0.3 to 3 g/10 minutes and a Dilution Index, Yd, of greaterthan 0°; and a core comprising polyethylene, with the proviso that thepolymeric material used to prepare said multilayer film is at least 90%by weight polyethylene based on the total weight of said polymericmaterial; said process comprising forming a package structure by placinga first layer of said multilayer film on top of a second layer of saidmultilayer film such that the second skin layer of said first layer isin contact with said second skin layer; applying heat and pressure to atleast one of said first skin layer of said first layer and said secondskin layer of said second layer wherein said heat and pressure issufficient to melt bond said second skin layer of said first layer tosaid second skin layer of said second layer. 7-11. (canceled)
 12. Aprocess to make a sealed package with a multilayer film comprising: afirst skin layer consisting of from 85 to 100 weight % of a high densitypolyethylene having a density of from 0.95 to 0.97 g/cc and a meltindex, I₂, of from 0.5 to 10 g/10 minutes; a second skin layerconsisting of from 85 to 100 weight % of a first linear low densityinterpolymer having a molecular weight distribution Mw/Mn of from 2.5 to4.0, a density of from 0.90 to 0.92 g/cc, a melt index, I₂, of from 0.3to 3 g/10 minutes and a Dilution Index, Yd, of greater than 0°; and acore comprising linear low density polyethylene having a density of from0.90 to 0.92 g/cc, with the proviso that the polymeric material used toprepare said multilayer film is at least 90% by weight polyethylenebased on the total weight of said polymeric material; said processcomprising forming a package structure by placing a first layer of saidmultilayer film on top of a second layer of said multilayer film suchthat the second skin layer of said first layer is in contact with saidsecond skin layer; applying heat and pressure to at least one of saidfirst skin layer of said first layer and said second skin layer of saidsecond layer wherein said heat and pressure is sufficient to melt bondsaid second skin layer of said first layer to said second skin layer ofsaid second layer. 13-17. (canceled)
 18. A process to make a sealedpackage with a multilayer film comprising: a first skin layer consistingof from 85 to 100 weight % of a high density polyethylene having adensity of from 0.95 to 0.97 g/cc and a melt index, I₂, of from 0.5 to10 g/10 minutes; a second skin layer consisting of from 85 to 100 weight% of a first linear low density interpolymer having a molecular weightdistribution Mw/Mn of from 2.5 to 4.0, a density of from 0.90 to 0.92g/cc, a melt index, I₂, of from 0.3 to 3 g/10 minutes and a DilutionIndex, Yd, of greater than 0°; and a core comprising medium densitypolyethylene having a density of from 0.930 to 0.95 g/cc, with theproviso that the polymeric material used to prepare said multilayer filmis at least 90% by weight polyethylene based on the total weight of saidpolymeric material; said process comprising forming a package structureby placing a first layer of said multilayer film on top of a secondlayer of said multilayer film such that the second skin layer of saidfirst layer is in contact with said second skin layer; applying heat andpressure to at least one of said first skin layer of said first layerand said second skin layer of said second layer wherein said heat andpressure is sufficient to melt bond said second skin layer of said firstlayer to said second skin layer of said second layer.
 19. A stand uppouch made according to the process of claim
 18. 20. The process ofclaim 18, wherein the core medium density polyethylene has a densityfrom about 0.935 g/cc to 0.945 g/cc.
 21. The process of claim 18,wherein said the core contains a layer of EVOH, with the proviso thatthe weight of said EVOH is from 0.5 to 5 weight % of the total weight ofpolymeric material used to prepare said multilayer film.
 22. The processof claim 18, wherein the multilayer film has from 3 to 11 layers. 23.The process of claim 18, wherein said first linear low densityinterpolymer is synthesized in a multi reactor polymerization system inthe presence of at least one single site catalyst formulation and atleast one heterogeneous catalyst formulation.
 24. The process of claim18, wherein the second skin layer consists of about 85 to 100 weight %of a first linear low density interpolymer having a molecular weightdistribution Mw/Mn of 2.5 to 4.0, and a density of about 0.905 to 0.917g/cc.
 25. A stand up pouch made according to the process of claim
 6. 26.The process of claim 6, wherein said core contains a layer of ethylenevinyl alcohol (EVOH), with the proviso that the weight of said EVOH isfrom 0.5 to 5 weight % of the total weight of polymeric material used toprepare said multilayer film.
 27. The process of claim 6, wherein themultilayer film has from 3 to 11 layers.
 28. The process of claim 6,wherein said first linear low density interpolymer is synthesized in amulti reactor polymerization system in the presence of at least onesingle site catalyst formulation and at least one heterogeneous catalystformulation.
 29. The process of claim 6, wherein the second skin layerconsists of about 85 to 100 weight % of a first linear low densityinterpolymer having a molecular weight distribution Mw/Mn of 2.5 to 4.0,and a density of about 0.905 to 0.917 g/cc.
 30. The process of claim 6,wherein the second skin layer has a melt index I₂ of about 0.5 to 1.5g/10 min.
 31. The process of claim 29, wherein the second skin layer hasa melt index I₂ of about 1.0 g/10 min.
 32. A form-fill-seal pouch madeaccording to the process of claim
 12. 33. The process of claim 12,wherein said second skin layer has a density of 0.905 to 0.917 g/cc. 34.The process of claim 12, wherein the multilayer film has from 3 to 11layers.
 35. The process of claim 12, wherein said first linear lowdensity interpolymer is synthesized in a multi reactor polymerizationsystem in the presence of at least one single site catalyst formulationand at least one heterogeneous catalyst formulation.